Nitride uv light sensors on silicon substrates

ABSTRACT

An ultraviolet light sensor and method of manufacturing thereof are disclosed. The ultraviolet light sensor includes Group-III Nitride layers adjacent to a silicon wafer with one of the layers at least partially exposed such that a surface thereof can receive UV light to be detected. The Group-III Nitride layers include a p-type layer and an n-type layer, with p/n junctions therebetween forming at least one diode. Conductive contacts are arranged to conduct electrical current through the sensor as a function of ultraviolet light received at the outer Group-III Nitride layer. The Group-III Nitride layers may be formed from, e.g., GaN, InGaN, AlGaN, or InAlN. The sensor may include a buffer layer between one of the Group-III Nitride layers and the silicon wafer. By utilizing silicon as the substrate on which the UV sensor diode is formed, a UV sensor can be produced that is small, efficient, cost-effective, and compatible with other semiconductor circuits and processes. The sensor may be configured to be sensitive to a specific subtype or subband of ultraviolet radiation to be detected by selecting a specific composition of said Group-III Nitride layers.

This application is a non-provisional of and claims the benefit of U.S.Patent Application No. 61/550,868 filed Oct. 24, 2011, the entiredisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to semiconductor devices, andmore particularly to a structure and method for forming Nitrideultraviolet (UV) sensors, including sensors for sensing one or more ofUVA, UVB and UVC radiation.

BACKGROUND

An ultraviolet sensor or detector absorbs UV radiation generally in thewavelength range between 100 nm to 400 nm and provides an outputindicative of the sensed UV radiation. The UV spectrum can be subdividedinto a number of different subbands, such as UVA, UVB and UVC. Thewavelength (photon energy) of these subbands of the UV radiation rangefrom 400 nm to 315 nm for UVA (3.1 eV to 3.94 eV), 315 nm to 280 nm forUVB (3.94 eV to 4.43 eV), and 280 nm to 100 nm for UVC (4.43 eV to 12.4eV).

Typically, UV sensors are very costly because they utilize exotic andexpensive wafer substrate materials, such as silicon carbide andsapphire wafers, which can be an order of magnitude more expensive thanthe silicon of which most semiconductors are typically manufactured.

SUMMARY

An ultraviolet light sensor and method of manufacturing thereof aredisclosed. The ultraviolet light sensor includes Group-III Nitridelayers adjacent to a silicon wafer with one of the layers at leastpartially exposed such that a surface thereof can receive UV light to bedetected. The Group-III Nitride layers include a p-type layer and ann-type layer, with p/n junctions therebetween forming at least onediode. First and second conductive contacts are arranged to conductelectrical current through the sensor as a function of ultraviolet lightreceived at the outer Group-III Nitride layer. The Group-III Nitridelayers may be formed from, e.g., GaN, InGaN, AlGaN, or InAlN. The sensormay include a buffer layer between one of the Group-III Nitride layersand the silicon wafer. By utilizing silicon as the substrate on whichthe ultraviolet sensor diode is formed, a UV sensor can be produced thatis small, efficient, cost-effective, and compatible with othersemiconductor circuits and processes. The sensor may be configured to besensitive to a specific subtype or subband of ultraviolet radiation tobe detected by selecting a specific composition of the Group-III Nitridelayers.

DRAWINGS

The above-mentioned features of the present disclosure will become moreapparent with reference to the following description taken inconjunction with the accompanying drawings wherein like referencenumerals denote like elements and in which:

FIG. 1 is a cross-sectional view illustrating the layers of anoperational Nitride UV GaN sensor diode formed on a silicon substrate inaccordance with one or more embodiments of the present disclosure thatis sensitive to UVA, UVB and UVC subbands.

FIG. 2 shows a graphical representation of a spectral response curve forthe Nitride UV sensor of FIG. 1 illustrating the External QuantumEfficiency {EQE} and the corresponding wavelength of such sensor.

FIG. 3 is a cross-sectional view illustrating the layers of anoperational Nitride UV InGaN sensor diode formed on a silicon substratein accordance with one or more embodiments of the present disclosurethat is sensitive to UVA, UVB and UVC subbands.

FIG. 4 is a cross-sectional view illustrating the layers of anoperational Nitride UVA only GaN sensor diode including a filter inaccordance with one or more embodiments of the present disclosure.

FIG. 5 is a cross-sectional view illustrating the layers of anoperational Nitride UVB AlGaN sensor diode formed on a silicon substratein accordance with one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings in which like reference number indicate like components. Thefollowing description and drawings are illustrative and are not to beconstrued as limiting. Numerous specific details are described toprovide a thorough understanding. However, in certain instances,well-known or conventional details are not described in order to avoidobscuring the description. References to one or an embodiment in thepresent disclosure are not necessarily references to the sameembodiment; and, such references mean at least one.

Reference in this specification to “an embodiment” or “the embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least an embodimentof the disclosure. The appearances of the phrase “in an embodiment” or“in one or more embodiments” in various places in the specification arenot necessarily all referring to the same embodiment, nor are separateor alternative embodiments mutually exclusive of other embodiments.Moreover, various features are described which may be exhibited by someembodiments and not by others. Similarly, various requirements aredescribed which may be requirements for some embodiments but not otherembodiments.

In general, the present disclosure is directed to various embodiments ofstructures and methods for the formation of UV, UVA, UVB and UVC sensorsfrom Group-III Nitride semiconductor P/N junctions forming diodes withengineered band edge selectivity of various UV frequencies.

In one or more embodiments, a structure and method are provided for theformation of UV, UVA, UVB and UVC sensors from Group-III Nitridesemiconductor P/N junctions forming diodes with engineered band edgeselectivity of various UV frequencies. Group-III Nitride semiconductors,including InN, GaN and AlN and their alloys, have a direct energy gapranging from 0.7 eV (InN) to 6.2 eV (AlN). The band gap can beselectively adjusted to be sensitive to the specific subtype or subbandof the UV radiation being detected. In one or more embodiments, theGroup-III Nitride semiconductor material comprises GaN, AlGaN, InGaN, orInAlN.

In one or more embodiments, a structure and method are provided for theformation of UV, UVA, UVB and UVC sensors from Group-III Nitridesemiconductor P/N junctions on a silicon substrate in order to provide ahighly reliable UV sensor with dramatically lower costs of formation andother advantages. By utilizing silicon as the substrate on which the UVsensor diode is formed, a UV sensor that is small, efficient andcost-effective can be produced. This device structure allows lower costand smaller packages for electronic assemblies that are furthercompatible with silicon substrates and other low cost substratesfrequently utilized in the semiconductor industry. The UV sensor of theinvention can, in some embodiments, be integrated on the same siliconwafer as other semiconductor circuits.

In one or more embodiments, a UV sensor comprising a GaN, InGaN, AlGaNor InAlN P/N junction formed on a silicon substrate in accordance withthe invention can be used in many applications and markets, such assmartphones that include functionality for detecting UV radiation levelsthat are harmful to the skin.

Referring now to FIG. 1, a block diagram is shown that illustrates thelayers of an operational Nitride UV sensor diode in accordance with oneor more embodiments of the present disclosure that is sensitive to UVA,UVB and UVC subbands. The UV sensor of FIG. 1 includes a p-type GaN toplayer 100, followed by an n-type GaN layer 120 which is formed on abuffer layer 130, all of which are formed on a silicon substrate wafer140. The buffer layer 130 assists with growing the GaN layers 100, 120on the silicon substrate wafer 140 so as to improve the quality and inturn the performance of the GaN layers 100, 120. Metal contacts 160 forthe sensor diode are formed on at least a portion of the opposingoutside surfaces of the Nitride UV sensor.

In one or more embodiments, the substrate wafer 140 comprises a siliconsubstrate in order to provide a highly reliable UV sensor withdramatically lower costs of formation than conventional UV sensors thatmade use of silicon carbide or sapphire wafers. By utilizing silicon asthe substrate wafer 140 on which the UV sensor diode is formed, a UVsensor in accordance with the present disclosure that is small,efficient and cost-effective can be produced. While silicon ispreferably used as the substrate wafer 140 for these advantages and itscustomary usage in the semiconductor industry, it is understood thatother low-cost substrates frequently utilized in the semiconductorindustry could be used in place of silicon in the various embodimentsdescribed herein, such as glass or the like.

FIG. 2 shows a graphical representation illustrating a spectral responsecurve for the Nitride UV GaN sensor of FIG. 1. In particular, FIG. 2illustrates dependencies of the External Quantum Efficiency {EQE} on thecorresponding wavelength of such sensor. FIG. 2 shows a UVA responsebelow 370 nm. Curve 210 represents a bias of 0 V, while curve 220represents a bias of 1.6 V.

Referring now to FIG. 3, a block diagram is provided that illustratesthe layers of an operational Nitride UV InGaN sensor diode formed on asilicon substrate in accordance with one or more embodiments of thepresent disclosure. In such embodiments, the UV sensor is designed to besensitive to UVA, UVB and UVC subbands. The structure of FIG. 3 includesa p-type In_(0.11)Ga_(0.89)N (or In_(0.38)Al_(0.62)N) top layer 300,followed by an n-type In_(0.11)Ga_(0.89)N (or In_(0.38)Al_(0.62)N) layer320 which is formed on a buffer layer of AlN 330, all of which areformed on a silicon substrate wafer 140. Metal contacts 360 for thesensor diode are formed on at least a portion of the opposing outsidesurfaces of the Nitride UV sensor. In one or more embodiments, thespecific alloy composition of In_(0.11)Ga_(0.89)N allows the various UVfrequencies for each of the UVA, UVB and UVC subbands to be detected.The specific composition of the Group-III Nitride semiconductor layersforming the P/N junction can be engineered to possess band edgeselectivity for the desired UV frequencies to be detected.

Referring now to FIG. 4, a block diagram is provided that illustratesthe layers of a working Nitride UVA only GaN sensor diode in accordancewith one or more embodiments of the present disclosure. The UVA sensorof FIG. 4 includes a filter (Al_(0.22)Ga_(0.78)N (orIn_(0.27)Al_(0.73)N) layer 450) that only allows the UVA subband to passthere through, where the specific composition of the Al_(0.22)Ga_(0.78)N(or In_(0.27)Al_(0.73)N) layer 450 is engineered for this purpose. Thefilter layer 450 is formed on a p-type GaN top layer of the diode 400,followed by an n-type GaN bottom layer of the diode 420. The diodelayers are formed on a buffer layer of AlN 430, which is formed on asilicon substrate wafer 440. Metal contacts 460 for the sensor diode areformed on at least a portion of the opposing outside surfaces of theNitride UVA sensor.

Referring now to FIG. 5, a block diagram is provided that illustratesthe layers of a working Nitride UVB AlGaN sensor diode in accordancewith one or more embodiments of the present disclosure The UVB sensor ofFIG. 5 includes a p-type Al_(0.22)Ga_(0.78)N (or In_(0.27)Al_(0.73)N)layer top layer of the diode 500, followed by an n-typeAl_(0.22)Ga_(0.78)N (or In_(0.27)Al_(0.73)N) layer bottom layer of thediode 520. The diode layers are formed on a buffer layer of AlN 530,which is formed on a silicon substrate wafer 540. Metal contacts 560 forthe sensor diode are formed on at least a portion of the opposingoutside surfaces of the Nitride UVA sensor.

In the various embodiments described herein, the metal contacts 160,360, 460, 560 are formed from any conductive materials used inaccordance with methods known to those skilled in the art ofmanufacturing UV sensors. In one or more embodiments, the top metalcontact on the UV sensor should be sized and formed so as to allow UVradiation to travel past the top metal contact to enter into the UVsensor, such as by forming the top metal contact on only a portion ofthe top surface of top diode layer, from Indium-Tin-Oxide or othersuitable semi-transparent or substantially transparent conductivematerial (e.g., NiAl) or by forming the contact in a grid formation.

In the various embodiments described herein, the buffer layers 130, 330,430, 530 are described as comprising AlN but it is understood that thebuffer layers may alternatively comprise other materials known to thoseskilled in the art to assist in the formation of the semiconductorlayers on a silicon substrate wafer. However, in one or more alternativeembodiments, it is understood that the Nitride UV sensors describedherein may be formed without the use of a buffer layer.

In one or more embodiments, the Group-III Nitride layers (or otherlayers) may be deposited using any number of known depositiontechniques, such as molecular beam epitaxy (MBE), metal-organic chemicalvapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), remoteplasma chemical vapor deposition (RPCVD), or any other appropriatedeposition method.

The above embodiments and preferences are illustrative of the presentinvention. It is neither necessary, nor intended for this patent tooutline or define every possible combination or embodiment. The inventorhas disclosed sufficient information to permit one skilled in the art topractice at least one embodiment of the invention. The above descriptionand drawings are merely illustrative of the present invention and thatchanges in components, structure and procedure are possible withoutdeparting from the scope of the present invention as defined in thefollowing claims. For example, elements and/or steps described aboveand/or in the following claims in a particular order may be practiced ina different order without departing from the invention. Thus, while theinvention has been particularly shown and described with reference toembodiments thereof, it will be understood by those skilled in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention.

1. An ultraviolet light sensor, comprising: a silicon wafer; a pluralityof Group-III Nitride layers adjacent to said silicon wafer, with one ofthe Group-III Nitride layers at least partially exposed such that asurface thereof can receive ultraviolet light to be detected, saidGroup-III Nitride layers comprising a p-type layer and an n-type layerwith p/n junctions therebetween forming at least one diode; and, firstand second conductive contacts arranged to conduct electrical current asa function of ultraviolet light received at said GaN layer.
 2. Theultraviolet light sensor according to claim 1, wherein said Group-IIINitride layers comprise a GaN layer.
 3. The ultraviolet light sensoraccording to claim 1, wherein said Group-III Nitride layers comprise anInGaN layer.
 4. The ultraviolet light sensor according to claim 1,wherein said Group-III Nitride layers comprise an AlGaN layer.
 5. Theultraviolet light sensor according to claim 1, wherein said Group-IIINitride layers comprise an InAlN layer.
 6. The ultraviolet light sensoraccording to claim 1, further comprising a buffer layer between one ofsaid Group-III Nitride layers and said silicon wafer.
 7. The ultravioletlight sensor according to claim 6, wherein said buffer layer comprisesAlN.
 8. The ultraviolet light sensor according to claim 1, wherein oneof said first and second conductive contacts is located so as to allowultraviolet radiation to travel past it.
 9. The ultraviolet light sensoraccording to claim 1, wherein at least one of said first and secondconductive contacts comprise a semi-transparent or substantiallytransparent conductive material.
 10. The ultraviolet light sensoraccording to claim 9, wherein said at least one of said first and secondconductive contacts comprises Indium-Tin-Oxide.
 11. The ultravioletlight sensor according to claim 9, wherein said at least one of saidfirst and second conductive contacts comprises NiAl.
 12. The ultravioletlight sensor according to claim 1, wherein said conductive contacts aremetal.
 13. The ultraviolet light sensor according to claim 1, whereinsaid silicon substrate is p-doped.
 14. The ultraviolet light sensoraccording to claim 1, wherein said Group-III Nitride layers comprise ap-type In_(0.11)Ga_(0.89)N top layer followed by an n-typeIn_(0.11)Ga_(0.89)N bottom layer, said bottom layer being layered on abuffer layer formed on a silicon substrate wafer.
 15. The ultravioletlight sensor according to claim 14, wherein said buffer layer comprisesAlN.
 16. The ultraviolet light sensor according to claim 1, wherein saidGroup-III Nitride layers comprise a p-type In_(0.38)Al_(0.62)N top layerfollowed by an n-type In_(0.38)Al_(0.62)N bottom layer, said bottomlayer being layered on a buffer layer formed on a silicon substratewafer.
 17. The ultraviolet light sensor according to claim 14, whereinsaid buffer layer comprises AlN.
 18. The ultraviolet light sensoraccording to claim 1, configured to absorb and respond to UVA radiationat a wavelength range between 400 nm and 315 nm.
 19. The ultravioletlight sensor configured as a UVA sensor according to claim 18, furthercomprising a filter of Al_(0.22)Ga_(0.78)N, and wherein said Group-IIINitride layers comprise a p-type GaN top layer followed by an n-type GaNlayer on a buffer layer formed on a silicon substrate wafer.
 20. Theultraviolet light sensor configured as a UVA sensor according to claim19, wherein said buffer layer comprises AlN.
 21. The ultraviolet lightsensor configured as a UVA sensor according to claim 18, furthercomprising a filter of In_(0.27)Al_(0.73)N, and wherein said Group-IIINitride layers comprise a p-type GaN top layer followed by an n-type GaNlayer on a buffer layer formed on a silicon substrate wafer.
 22. Theultraviolet light sensor configured as a UVA sensor according to claim21, wherein said buffer layer comprises AlN.
 23. The ultraviolet lightsensor according to claim 1, configured to absorb and respond to UVBradiation at a wavelength range between 315 nm and 280 nm.
 24. Theultraviolet light sensor configured as a UVB sensor according to claim23, wherein said Group-III Nitride layers comprise a p-typeAl_(0.22)Ga_(0.78)N top layer, followed by an n-type Al_(0.22)Ga_(0.78)Nbottom layer on a buffer layer formed on a silicon substrate wafer. 25.The ultraviolet light sensor configured as a UVB sensor according toclaim 24, wherein said buffer layer comprises AlN.
 26. The ultravioletlight sensor configured as a UVB sensor according to claim 23, whereinsaid Group-III Nitride layers comprise a p-type In_(0.27)Al_(0.73)N toplayer, followed by an n-type In_(0.27)Al_(0.73)N bottom layer on abuffer layer formed on a silicon substrate wafer.
 27. The ultravioletlight sensor configured as a UVB sensor according to claim 26, whereinsaid buffer layer comprises AlN.
 28. The ultraviolet light sensoraccording to claim 1, configured to absorb and respond to UVC radiationat a wavelength range between 280 nm and 100 nm.
 29. The ultravioletlight sensor according to claim 1, configured to absorb and respond toultraviolet radiation at a wavelength range between 100 nm to 400 nm.30. The ultraviolet light sensor according to claim 1, wherein at leastone further semiconductor circuit, in addition to a circuit between saidelectrical contacts, is formed on said silicon wafer.
 31. A method formanufacturing an ultraviolet light sensor, comprising: forming Group-IIINitride layers adjacent to a silicon wafer such that one of saidGroup-III Nitride layers is at least partially exposed, whereby said oneof said Group-III Nitride layers can receive ultraviolet light to bedetected, said Group-III Nitride layers comprising a p-type layer and ann-type layer with p/n junctions therebetween forming at least one diode;and, forming first and second conductive contacts such that saidcontacts conduct electrical current as a function of ultraviolet lightreceived in at least one of said Group III Nitride layers.
 32. Themethod for manufacturing an ultraviolet light sensor according to claim31, wherein said step of forming Group-III Nitride layers comprisesselectively adjusting a band gap to be sensitive to a specific subtypeor subband of ultraviolet radiation to be detected by selecting aspecific composition of said Group-III Nitride layers.
 33. The methodfor manufacturing an ultraviolet light sensor according to claim 31,wherein said step of selectively adjusting a band gap comprisesselectively adjusting a band gap to be sensitive to UVA radiation. 34.The method for manufacturing an ultraviolet light sensor according toclaim 31, wherein said step of selectively adjusting a band gapcomprises selectively adjusting a band gap to be sensitive to UVBradiation.
 35. The method for manufacturing an ultraviolet light sensoraccording to claim 31, wherein said step of selectively adjusting a bandgap comprises selectively adjusting a band gap to be sensitive to UVCradiation.
 36. The method for manufacturing an ultraviolet light sensoraccording to claim 31, wherein said step of forming first and secondconductive contacts comprises forming such contacts on at least aportion of opposing outside surfaces.
 37. The method for manufacturingan ultraviolet light sensor according to claim 31, wherein said step offorming Group-III Nitride layers comprises forming an n-type GaN layeron a buffer layer.
 38. The method for manufacturing an ultraviolet lightsensor according to claim 31, wherein said step of forming Group-IIINitride layers comprises growing a Group-III Nitride layer.
 39. Themethod for manufacturing an ultraviolet light sensor according to claim31, wherein said step of forming Group-III Nitride layers comprisesdepositing said Group-III Nitride layer by molecular beam epitaxy. 40.The method for manufacturing an ultraviolet light sensor according toclaim 31, wherein said step of forming Group-III Nitride layerscomprises depositing at least one Group-III Nitride layer bymetal-organic chemical vapor deposition.
 41. The method formanufacturing an ultraviolet light sensor according to claim 31, whereinsaid step of forming Group-III Nitride layers comprises depositing atleast one Group-III Nitride layer by hydride vapor phase epitaxy. 42.The method for manufacturing an ultraviolet light sensor according toclaim 31, wherein said step of forming Group-III Nitride layerscomprises depositing at least one Group-III Nitride layer by remoteplasma chemical vapor deposition.
 43. The method for manufacturing anultraviolet light sensor according to claim 31, wherein said step offorming first and second conductive contacts comprises forming at leastone of said contacts as a grid so as to allow ultraviolet radiation totravel past said at least one contact to a top layer of said Group-IIINitride layers.